Point Sal Inner Shelf Experiment (PSIEX): Spatial and Temporal Variability of Subtidal and Tidal Temperature and Current Structure

Field observations of temperature and velocity were obtained with high temporal and vertical resolution using cross- and alongshore arrays deployed in the inner shelf that extended from edge of the surf zone to 50m water depth for 43 days in the summer of 2015 at Point Sal, CA. The experimental design focused on describing the spatial, including the vertical, and temporal scales of temperature variability for the inner shelf induced by offshore process (e.g., subtidal flows, internal tidal bores, and solitons) and surf zone processes (e.g., rip currents) that were additionally modified by the presence of rocky points and a large offshore subaqueous rocky outcrop. Here observations are focused on the evolution of the subtidal and tidal variability. Both internal tidal waves (bores) of depression and elevation were observed that transport masses of warm and cold water toward the nearshore and ultimately into the surf zone. Cold-water bores tend to stratify the water column; whereas warm-water bores result is an isothermal water column. There is a large-scale subtidal temperature coherence resulting in periods of warming and cooling that vertically change the location of the thermocline. Similarly, there is large-scale coherence with tidal bores as they propagate into shallow water. However, the cross-shore tidal bore coherence decreases rapidly over a relatively short distance, which is believed related to the irregular bathymetry. The magnitude of the internal tidal bores differs between the west and north facing shorelines of Pt. Sal. There is a net subtidal transport to the south that induces increased variability on the north side of the rocky points. The barotropic tides are oriented along the coast along the isobaths with near linear excursions, whereas the baroclinic tidal movements are more elliptical. PSIEX was supported by the Office of Naval Research.